1. Field of the Invention
The present invention relates to a bonding layer for bonding resin on a copper surface. More specifically, this invention relates to a bonding layer for bonding resin on a copper surface, which is used for various types of electronic components such as a printed wiring board, components to be mounted on a semiconductor, liquid crystal devices, electroluminescent elements and the like.
2. Related Background Art
Multilayer wiring boards in common use are produced in the following manner. That is, an inner-layer substrate having a conductive layer of copper on its surface is press-laminated to another inner-layer substrate and copper foil so as to sandwich a prepreg between them. Electrical connections between the respective conductive layers are established by way of through-holes, i.e. piercing holes whose walls are plated with copper. In order to enhance adhesion to the prepreg, a needle-like layer of copper oxide that is referred to as a black oxide or a brown oxide is formed on the copper surface of the inner-layer substrate. In this method, the needle-like layer of copper oxide cuts into the prepreg to produce the anchoring effect, thereby enhancing adhesion.
While exhibiting excellent adhesion to the prepreg, the layer of copper oxide dissolves and discolors when brought into contact with an acidic liquid in a process of plating the through-holes, and thus is likely to cause a defect called haloing, which is problematic.
With respect to this problem, as an alternative to the method using a black oxide or a brown oxide, a method in which a tin layer is formed on a copper surface of an inner-layer substrate has been proposed as in EP Publication No. 0 216 531 A1 and JP 4(1992)-233793 A. Further, JP 1(1989)-109796 A proposes that a copper surface be plated with tin and then further treated with a silane coupling agent so that adhesion between copper and resin is enhanced. Further, JP2000-340948 A proposes to form a copper-tin alloy layer on a copper surface so as to enhance adhesion between copper and resin. Further, it also is proposed that the copper surface be roughened by etching so as to produce the anchoring effect.
However, in each of the above-mentioned methods in which a tin layer or a copper-tin alloy layer is formed on a copper surface, with respect to a so-called hard resin, which is a type of resin having a high glass transition temperature, the effect of enhancing adhesion may not be attained sufficiently, which has been disadvantageous. Further, in the above-mentioned method described in JP 1(1989)-109796 A, tin plating causes copper to be eluted into a plating solution, resulting in the narrowing of wiring. Moreover, when in use, silane coupling agents are hard to handle, which is problematic. Further, adhesion to resin is not attained sufficiently.